Wheelbarrows of different design and configuration comprise a container, two handles for lifting and pushing, one or two wheels mounted at the front of the container extending downwardly therefrom, and two legs at the rear of the container, also extending downwardly therefrom. When the wheelbarrow is at rest, balancing and stability is maintained by the two rear legs and the one or two front wheels. The stability of the wheelbarrow in this case is determined by the center of gravity (CoG) of the bulk material in the wheelbarrow and of the wheelbarrow's geometric shape that is defined by the contact points of the two legs and the one or two wheels with the ground. The two legs and one wheel define a triangle, that is, a triangle of stability, whereas two legs and two wheels define a trapezoid. It is well-known that as long as the CoG falls within this triangle or trapezoid of stability, the wheelbarrow is in a stable state. However, as the wheelbarrow is lifted and is moved forwardly or tilted laterally, the CoG also moves from its initial position forwardly and/or laterally, accordingly. Similarly, as the wheelbarrow is lifted and it is moved forwardly or tilted laterally, the geometric shapes that define stability i.e. triangle or trapezoid, change shape because they are now defined by the legs of the operator and the contact between the wheel or wheels with the ground. In such case, the CoG often falls outside the newly defined stability geometric shape.
To lift a loaded wheelbarrow, a substantial lifting force is required that depends on the actual load, the position of the CoG with respect to distance between the CoG and the wheel axle, and on the distance between the handles and the wheel axle, as they are defined by established equations of the lever. When the wheelbarrow is pushed laterally to make a left or a right turn, as it tilts to the left or to the right the CoG moves to the left or to the right, accordingly.
In the case of a single flat wheel, the CoG tends to move outside the triangle of stability and therefore in addition to the pushing force, a differential counterbalancing force is required, which acts on the wrists of the operator. If the load is substantial, the tilting unbalancing force may be stronger than the counterbalancing force and the result is disastrous; the wheelbarrow goes out of balance.
In the case of two wheels mounted on the sides of the container, when the wheelbarrow is lifted, a lifting force is required as in the previous case, with the amount of force still depending on the load, the CoG position with respect to distance between the CoG and the wheel axle, and on the distance between the handles and the wheel axle. However, when the wheelbarrow is pushed to make a left or right turn, the wheelbarrow is not as easy to maneuver because the two front side wheels are fixed and they drag on the ground unevenly due to the unequal radii of the turn. In an automobile, this is ameliorated by turning the two front wheels accordingly to equalize the radii of the arc of the turn. Thus, although tilting is not as big of a problem as in the single wheel case, turning the wheelbarrow by a single operator is particularly bothersome if the load is substantial and if the turn is sharp. It is the differential dragging of the two wheels in this case that requires additional effort by the operator to easily maneuver and control the two-wheel wheelbarrow.
Some of the above shortcomings have been addressed by various two wheel-design wheelbarrows and by various single wheel-design wheelbarrows with a ball shape. Examples are U.S. Pat. Nos. 4,058,344; 3,827,369; 2,967,058, and 6,193,265 B1. However, none of these or others, discloses or suggests a multipurpose wheelbarrow design, which, with minimal force and effort, is easily maneuverable, controllable, and has superior stability under all modes of operation, such as forward pushing, tilting and turning, and loading and unloading.
Therefore, there is a need for a wheelbarrow that employs the combined principles of physics for levering, for stability of wheeled vehicles during forward motion and during turning; an ergonomic handle design with multiple grips for easy lifting and unloading and a self-adjustable barrel-shaped ellipsoidal wheel that exhibits stability during forward motion, turning and lateral tilting, superior maneuverability and control and require minimal lifting and forward pushing as well as laterally counterbalancing forces by the operator.